Ferrite based antennae for launching Alfvén waves.

ABSTRACT

Whistler and Alfvén waves are known to scatter mirror-trapped electrons and protons into the loss cone of the earth's dipole magnetic field. An array of satellites with properly phased antennas can be used to artificially reduce the flux of energetic particles from regions where their flux has been naturally or artificially pumped. In any space based system, the power required to drive antennas is at a premium. We present here experimental evidence that the efficiency of an antenna can be greatly enhanced with the use of ferrite cores with high relative magnetic permeability µ. Ferrite-based antennas were constructed to launch Alfvén waves in a magnetized plasma. The wave magnetic field of shear Alfvén waves launched with a ferrite core was by the magnetization factor µ larger than that of a similar antenna without a ferrite. Combining multiple ferrite antennas allowed control of the injected perpendicular wavelength. This novel technique can be used to efficiently launch low frequency waves with amplitude above the threshold required for nonlinear triggering.